A number of the emotional posts from Reubens' friends indicate he got joy out of celebrating the special days of others and would "bombard" those he loved with messages annually.

According to author Andrew Mayne, Reubens -- who died at the age of 70 following a private, six-year battle with cancer -- "kept birthday reminders for everyone he knew" and was steadfast in sending out greetings. "I watched him send a dozen in one sitting," added Mayne, "He was a very thoughtful person."

"Everyone I know received countless nonsensical memes from Paul on their birthday, and I mean EVERYONE," tweeted Conan O'Brien, something which became apparent as more tributes continued to flow in.

Both Ricki Lake and Modern Family's Eric Stonestreet shared their most recent birthday videos to social media, highlighting how special he made them feel with the tradition.

"I am shaking with disbelief and unbearable sadness at this news. 💔 I am choosing to share this personal video my friend, of almost 3 decades made for my birthday. Paul Reubens was one of my absolute favorites," Lake captioned her video (above). "Such a unique and incredible creator and talent but also a gracious, loyal and absolutely hilarious friend. The world will not be the same without him. Rest in peace, dear Paul. ♥️"

Stonestreet said Reubens would sent "20 funny gifs" to him on his special day, noting that he was "just one of the many people he made feel special" on their birthdays. "I'm thankful I was one of them," he continued, sharing the last video he got this year. "I'll keep it forever," Eric concluded.

"He never forgot a birthday," said Jimmy Kimmel, praising Reubens for sharing "his genuine delight for silliness with everyone he met."

The Walking Dead alum Norman Reedus, meanwhile, said Reubens was the first person to send him cards for Christmas, birthday, Valentine's Day and New Year's Eve "every single year," thanking him for "all the laughs."

Jane Lynch shared screen shots of the memes he sent on her most recent birthday just two weeks ago. "Goodbye sweet friend," she added.

"Every year, my friend Paul would bombard me with texts, emails & occasionally videos wishing me a 'Happy Birthday.' His Christmas cards were legendary," wrote WWE's Corey Graves. "I grew up a fan of Pee Wee. I was lucky to become friends with Paul Reubens. May the laughter he gave us all live on forever."

Mosaic costar Garrett Hedlund said "no birthday will be the same" now that he's gone, explaining that "even if it was a quiet one, it wasn't quiet from you." He also recalled all the memes and "heartfelt messages" Reubens would send each year, promising to "still laugh" in his honor.

Bill & Ted writer Ed Solomon, who also worked with Reubens on HBO's Mosaic, called the actor "one of the kindest souls I've ever known" -- and said that "every year since" they filmed the TV series he'd "head from him on my birthday & on every holiday."

Another person who showed off their texts from Paul was Patton Owalt, who wrote, "On my birthday this year, Paul sent me — and I mean he did this ALL DAY — GIFs of people getting hit in the face with cake. Miss you, man."

Big Top Pee-wee star Penelope Ann Miller called it a "treat" to not only work with Reubens, but also to become his friend. "I will miss his Christmas cards and birthday wishes and making us all laugh," she continued, calling him "the sweetest man."

SNL alum and founding member of The Groundlings Laraine Newman said the pair had been friends going all the way back to Cal Arts in 1973, calling him the "kind of friend that you can text out of nowhere or have a 3 hour lunch with." She added, "And don't get me started on the birthday texts - he sent them ALL DAY. I feel sick."

Chucky star Christine Elise also confirmed the texts came nonstop, while also praising the "cutest xmas cards" he sent for the holidays. "These two things were highlights in my life," she wrote, saying she "never never stopped feeling awestruck that he even knew who I was - let alone that he treated me like a friend."

Other stars to mention his birthday messages included Cheri Oteri, fellow Cal Arts alum David Hasselhoff, Video game developer Randy Pitchford and True Blood star Deborah Ann Woll -- who only met Reubens once in person at a premiere, but still made his list of greetings.

See their posts below.

And click here for more celebrity tributes following Reubens' death.